The present invention relates to a heat exchanger for hot air generator and boiler.
Heat exchangers are devices that are normally used in industrial or domestic systems to modify the temperature or the state of fluids, e.g. air or water. The principle they are based on is the transmission by conduction of heat through a wall or a membrane, so that two fluids tend to reduce the mutual temperature difference by generating a thermal flow that tends to warm the colder fluid and to cool the warmer fluid. The temperatures obtained at the end of such process vary depending on the physical and chemical characteristics of the fluids (air, water or others) and of the wall or membrane (having high or low thermal conductivity), on the geometry of the membrane surface (a larger slotted wall generally leads to a greater amount of heat exchanged) and on the flow characteristics (forced or natural convection, presence of turbulences).
In this way, the temperature of a fluid (“working fluid”) may be modified by forcing the heat exchange with another fluid (“exchange fluid”), a large amount of which is available at a temperature suitable to bring the working fluid to the requested temperature. When the heat exchange is over, the working fluid reaches the requested temperature, whereas the exhausted exchange fluid no longer allows the requested heat exchange and must therefore be expelled.
For example, if the working fluid needs to be heated, a heat exchange with fumes obtained by combustion from a burner may be carried out. To put such a process into practice, it is possible to use a heat exchanger comprised of:                a combustion chamber to generate high temperature fumes;        a tube bundle for the thermal exchange between the fumes and the working fluid;        a collection chamber for the exhausted fumes;        connectors between the combustion chamber and the tube bundle and between the latter and the fume collection chamber;        a discharge flue in connection with the fume collection chamber.        
More generally, a generic heat exchanger comprises:                a combustion chamber;        a slotted wall between the exchange fluid and the working fluid;        an expulsion chamber for the exhausted exchange fluid;        connector elements between the various components.        
Even though the physical principle the heat exchange technique is based on is very simple, there occurs a great difficulty in assembling the exchanger, because the constituent elements and the connector elements are numerous and different; their construction requires the use of a lot of machinery and equipment and of skilled labour.
Moreover, the need to achieve high efficiency in terms of exchanged heat in relation to the size of the heat exchanger leads to force winding paths for the exchange fluid, by inserting devices adapted to obtain a turbulent flow, which further increase the complexity of the heat exchangers.
Finally, because of the heat exchanger assembling complexity, it is rather difficult to modify the exchangers once these have already been constructed.